When sailing at night on watch I always have difficulty keeping awake and drift off for a few seconds/ hour and there is a number of marine
timers on the market quite expensive around AU$150.00 and not very adjustable at all.
I recently found Domestic digital 100 minute timer which is quite useful as you can set the interval up to 100 minutes and it times down and just start it again when the alarm
goes off, Its loud enough to wake you if you does off and must be reset to turn off the alarm
. It can also time down and stop and start again. Has a touch screen
and reasonably waterproof Made by Propert, a division of Supertex Industries in Australia
, not shown on their website that I could find,a real gem for under AU$10.00